Field
This invention relates generally to a drive chain which forms a rigid circular arc and, more particularly, to a drive chain designed to be used as an actuator for a hinge, where the chain includes links with offset pivot pins and abutment surfaces which cause the chain to form a rigid circular arc concentric with the rotational axis of the hinge, such that the chain can be used to drive the hinge in either direction.
Discussion
Spacecraft often employ various types of structures, such as reflectors, antenna arrays, sensors, etc., that must be deployed away from the spacecraft on a boom when the spacecraft is on orbit or in space. These booms typically employ one or more hinges that allow the boom and the structure to be folded or stowed into the spacecraft envelope or fairing during launch, and then be unfolded in space to the deployed position. In certain designs for larger structures, such as antenna reflectors, the boom and hinges are very robust to provide the desired pointing stiffness so that the structure remains pointed in the proper direction for a particular mission requirement. Various techniques are known in the art for unfolding or deploying the boom, including the use of motors, preloaded springs and other types of actuators.
A certain class of boom hinges are “clam-shell” designs that include two hinge halves. These boom hinges typically autonomously rotate from the stowed position when the antenna is in the spacecraft for launch to the deployed position when the spacecraft is in space. One known type of actuator for such boom hinges includes a linkage, such as a four-bar linkage, to reversibly open or close the hinge.
Hinge actuator designs for the boom hinge described above may be problematic in that if the boom hinge has a large rotation angle, for example 180°, from the stowed position to the deployed position, the links have to be so long that they need to pass through slots provided in the boom and hinge body wall when they are rotated through the deployment sequence. These slots reduce the structural integrity of the hinge, possibly to an unacceptable level. Also, the length of the links must be further increased with a corresponding decrease in efficiency if the boom pieces need to be spaced apart when stowed, i.e., if there is a significant offset between the hinge line and the boom and hinge center line. A need exists for a hinge actuator for a spacecraft boom that provides the necessary structural integrity and robustness but does not suffer the deficiencies of hinge actuators currently existing in the art.